Auto-thermal cracking is a known process for the production of olefins. An example of such a process is described in EP-A-0 332 289. In this process, a hydrocarbon and an oxygen-containing gas are contacted with a catalyst, which is capable of supporting combustion beyond the fuel rich limit of flammability. The hydrocarbon is partially combusted, and the heat produced is used to drive the dehydrogenation of the hydrocarbon feed into olefins.
In the auto-thermal cracking process the hydrocarbon and the oxygen-containing gas may be uniformly mixed and preheated prior to contacting the catalyst. However mixing and preheating the hydrocarbon and oxygen-containing gas becomes problematic if it is desired to carry out the process at elevated pressure due to flammability constraints. Thus, it becomes desirable to reduce the time between forming the mixture of hot gaseous reactants and contacting the mixture with the catalyst.